You have such an awesome last name, you are lucky! JackJustin is pretty awesome, his brother deserves equal. I am afraid the rhyming just is too much. Also, Jack is nicknamey, and Augustus is really formal. I assume you would call him Gus? Jack and Gus is a cool match. You could put it in the middle, I don't think I'd mind it there so much. August is pretty handsome and I really love Augusten. AugustenJustice is a wildly handsome name. I can also see Ace as a nn btw, maybe especially with a C middle name, which would be another cool tie in to Jack Champion...